I saw this on the 80 Percent Mental blog:
“I cannot underestimate how important regular exercise is in improving the function and performance of the brain.” Ratey writes. “Exercise stimulates our gray matter to produce Miracle-Gro for the brain.” That “Miracle-Gro” is a brain chemical called brain-derived neurotropic factor, or BDNF. When we exercise, our working muscles send chemicals into our bloodstream, including a protein known as IGF-1.
Several other studies found a correlation between fitness and grades.
“The exercise itself doesn’t make you smarter, but it puts the brain of the learners in the optimal position for them to learn,” Ratey said. “There’s no way to say for sure that improves learning capacity for kids, but it certainly seems to correlate to that.”
I guess that undermines the stereotype of the “dumb jock.”